The treatment of waste water is a problem which occurs mainly in suburban and rural zones where there may or may not exist a municipal drainage system to collect the waste water coming from dwellings and offices; it is then not properly treated in a waste water treatment plant, resulting in the untreated water being poured directly into an aquifer.
A variety of applications have been developed to solve this problem, one being the septic tank. A septic tank has the advantage of taking up little space as well as internally containing the elements which treat the waste water in a short time, without requiring external energy, and without exerting a rigid control over the processes, thus being highly individual systems.
Most of the waste water treatment plants use electromechanical equipment and are aerobic. They require high operation and maintenance. Because of this, even though their acquisition cost is relatively low and they use little space while extracting much sludge, they are more appropriate for more urbanized areas since their operational and control complexity cause them to be operative failures in suburban or rural zones.
Due to these kinds of problems, a type of equipment with low operation was designed which guarantees, even in the worst cases, an intermediate level of treatment. It also has the advantage of absorbing the peaks of the influent because it implements a better anaerobic process and has a greater retention time. It also has the possibility of obtaining bio-gas and a low production of sludge which can be used utilized afterwards.
In Mexico, one of the products currently available on the market is a septic tank which consists of a tank made of a plastic material. It has a filter fixed to the lid of the tank on the inside. It also has a feeding pipe and a discharge tube which comes out of the filter in such a way that the water comes into the tank, goes through the filter and overflows through the discharge tube once it has reached a certain height, attempting to imitate my patent No PA/a/1998/010893.
One of the closest prior designs is in the application for international patent WO02006/091064 which I created where the septic tank is a body formed by three sections, where the central part has a cylindrical section, the lower section has the form of a frustum pointing downwards and the upper section is also a frustum which has some triangular shaped projections whose hypotenuses are adjacent to the wall of the tank. These projections are placed in opposite directions making them rectangular in shape at the top. The sides of the triangle are perpendicular and the upper side of the triangle is horizontal.
In this invention, the feeding is done laterally through a horizontal tube which reaches the central part of the tank or septic pit. A duct connected perpendicularly to the end of this tube reaches the lower part of the tank without touching its bottom. (This is done in order to put the new water in contact with the anaerobic microorganisms which are part of the process)
This invention also has a duct which lets out the treated effluent. The diameter of this duct is smaller than the diameter of the feeding tube and this duct is placed at a lower height than the feeding tube. In the central part of the tank there is a cylindrically shaped filter which is placed in the center and in the lower part of the lid of the tank; the filter has filtering material up to the same height as the output tube of the effluent; the filter is crossed by feeding ducts and output ducts on its walls.
Additionally, the tank has a duct which extends from the upper part of the tank to the lower part without touching the bottom of the tank. This tube is placed in an inclined position in such a way that it practically reaches the bottom of the conical section without touching the bottom, and in the upper part it connects to a sludge discharge pipeline which has a horizontal shunt and which is located at a lower height than the output of the treated effluent and of the feeding input.
The advantages of this invention can be summarized as follows: it is a waterproof self-cleaning tank which does not require sludge extraction equipment although its design includes a duct which would allow this operation in case the self-cleaning tube was to become obstructed.
The patent application I wrote, publication WO2010/093232, relates to a septic tank with a self-cleaning filter and retro-feeding device and further includes a decanter and a skimmer.
The U.S. Pat. No. 5,227,061 by Robert D. Bedsole pertains to an apparatus which separates pollutants from fuel, with a cylindrical structure in its upper part and conical body in its lower part. The equipment has a curved feeding nozzle placed in the periphery of the pollutant separator which produces a centrifugal effect similar to that produced in centrifugal separators. The lower part of the separator is a water and solids collector which traps them in the filter where they accumulate and fall to the bottom section of the collector; meanwhile, since they are lighter, the fuel particles remain suspended and flow upwards through the center of the fuel/pollutants separator. However, this invention as it has been described above is not linked to the present invention because, to begin with, it is not self-cleaning and it requires high pressure in order to function.
The German patent application DE-102005027509 relates to a filter for a mixture of suspended solids. This invention has a container which rotates on a central axis, and has a tangential input. The suspension entering the container is thus subjected to both tangential and axial forces. A secondary vortex is formed in the center with the same tangential direction but with opposite axial component. The container is comprised of a filter assembly with a number of filtering elements placed in the barrier between the primary and secondary vortexes, facilitating the interaction among them. This separator requires a rotary movement, energy and a motor that powers the rotational movement. Therefore, it is not a static separator, which the separator of the present invention is.
The U.S. Pat. No. 4,918,426 comprises a water purification system which consists of an outer container, an input duct and an output duct. It also refers to the existence of a filtering element, but it never states that the system is self-cleaning or that it has a system to extract the separate solids; therefore, this invention also does not directly relate to the present invention.
The German application patent DE 19914674 refers to filtering equipment which requires a rotational movement to obtain filtration; hence, it does not solve the problem of finding equipment which can be used in rural communities as it requires high costs for energy and maintenance.
Although the document EP0300910 refers to filtration equipment, it is oriented to a liquid-gas separation and not a liquid-solids separation. This invention has a sedimentation tank which contains a filtering cartridge and a firmly attached outer casing which has an input and an output for the fuel. It is worth noting that this invention does not have any way to remove solids, as this is not its objective. Therefore it cannot be considered a state-of-the art separator even though it serves the purpose of fluids separation.
The U.S. Pat. No. 2,514,366 pertains to a filter which has similar elements to those mentioned in the present invention but it fails to be self-cleaning and needs to have the screw at the bottom of the tank removed in order to drain the sediments. Installation, therefore, must be at a certain height above the ground, or adding an access channel to clean the sludge would be required.
The patent application GB 2374297 comprises a sedimentation system where the sedimentation tank is specifically placed among a set of elements and which has a feeding tube that inputs the liquid tangentially. The tank has a tube at the bottom to drain the sediments as well as a tube to separate clear water. This system, in addition to being complex due to its large number of interconnected elements, also fails to solve the problem of having a self-cleaning septic tank, as its tank is drained by gravity. A gravity draining system implies that the tank has to be in an elevated position; whereas the tank of the present invention is designed to be buried which will enable it to drain solids through its upper part.
The European patent EP-0965375 refers to a tank which separates solids from a solids-liquids mixture. It is important to note that this invention requires the liquid to be pumped from the bottom of the tank, which means it does not allow the liquids to come out by the simple process of being at different levels, as does the present invention. It is important to point out that the flat bottom design of the tank does not guarantee an adequate collection of the solids to the drain, and that the spiral, even when it helps the solids collect, constitutes a barrier which permits the flow of the solids only if they have enough speed to be dragged to the drain.
The document ES-2089185 T3 relates to a tank to purify waste water, but even with a cylindrical body and a conical bottom, it, too, fails to solve the self-cleaning problem, and would therefore require the installation of a drainage tube and valves at the bottom of the tank for drainage purposes.
The Japanese patent JP-11333210 is a sedimentation tank which has an inner body to separate sludge. The water comes in through a tube which takes the water to the center of the tank and to the center of the sludge separation body which has the shape of an inverted cone positioned to oppose the conical shape of the bottom of the separation tank, thus creating a narrow slot in the periphery of the tank through which only the clarified water can pass while the debris gets trapped inside the conical body. This invention has an internal peripheral channel in the upper part, where the clarified water is collected and extracted by a pipeline. Again, the difference with this invention is that it not only is not a self-cleaning filter, it does not have a filter at all. In this invention, the level of the sludge will increase gradually ultimately requiring its extraction by mechanical means.
As the aforementioned information shows, there does not currently exist a piece of commercial equipment incorporated into one body which can carry out all the functions of solids-liquid separation, filtering and bio-digestion, and filtering and solids drainage without requiring any kind of support from mechanical means.
These data were obtained from a pilot test in which livestock waste water was treated.